The boy headmaster Philip Lawrence died trying to save has been jailed for carrying a pistol.
Philip Lawrence died protecting Njoh
William Njoh, 21, was sentenced to four-and-a-half years' imprisonment for carrying a gun to London's Notting Hill Carnival last year.
He was just 13 when Mr Lawrence was stabbed to death trying to protect him from a gang outside the St George's Roman Catholic School in Maida Vale, west London.
Njoh waved at Mr Lawrence's widow Frances, who blew him a kiss as he was led down to the cells at the Old Bailey on Friday.
The court heard his life had been blighted by the attack and having to give evidence in the murder trial.
I accept that you may have had a difficult and traumatic adolescence
His family had to move house and were put under police protection for fear of reprisals.
Njoh told the court: "I had to keep my identity from the other kids. There were people who did not approve that I was going to give evidence in a trial."
He dropped out of school at 15 and was sentenced to two years in a young offenders institution in 1998 for robbery.
Wary and fearful
Last year police found him carrying a Browning pistol and a bullet when he was searched at the Notting Hill Carnival.
He was convicted of firearms offences in January.
A psychiatric report said his experiences may have made Njoh "wary and fearful of others".
The judge, Recorder Peter Rook QC, said: "I accept that you may have had a difficult and traumatic adolescence."
But he said the pistol, even though it was unable to fire, would have caused terror at the carnival.
Outside court Mrs Lawrence said she felt sorry for Njoh.
She said: "I have to see what William would like, but I would like to visit him in prison.
"I feel he does need boundaries - but they are not prison walls."